In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In the third-generation system, it is possible to achieve a transmission rate of about maximum 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. In a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. In the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study as well (for example, LTE-Advanced (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band for LTE specifications, which is 20 MHz, to approximately 100 MHz.
LTE-A supports a system band of maximum 100 MHz, which is formed with a plurality of fundamental frequency blocks (hereinafter referred to as “component carriers” (cells) (CCs)), by carrier aggregation. In LTE-A, a heterogeneous network (hereinafter referred to as “HetNet”) configuration, which places significance on the local area environment, is under study. A HetNet is a layered network, which overlays cells of various forms such as pico cells, femto cells and relays (small cells), in addition to a conventional macro cell (large cell).
In LTE-A, uplink reference signals are enhanced, and the DM-RS (Demodulation-Reference Signal), which is used in channel estimation upon demodulation of the PUSCH (Physical Uplink Shard Channel) signal and the PUCCH (Physical Uplink Control Channel) signal and so on, is defined. This DM-RS is time-multiplexed and transmitted with RBs (Resource Blocks) that transmit the PUSCH signal/PUCCH signal. For example, in the PUSCH, the DM-RS is multiplexed over the third SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbol in each slot.